Ductility is a mechanical property used to describe the extent to which a material can be deformed plastically under stress without fracturing. When a low level of stress is applied, the deformation may be elastic, whereby on removal of the stress the workpiece returns to the shape it had before the stress was applied. At increasing levels of applied stress, the deformation becomes plastic. Beyond a certain level of applied stress, the workpiece fractures. The ductility of the workpiece, therefore, is related to the difference between the stress applied at fracture and the stress applied when deformation first becomes plastic.
Ductility of alloys is an important consideration for the selection of materials to be used in processes requiring forming and working of the alloys. In automobile manufacturing, for example, body panels must be formed into complex shapes with very precise specifications, often by extensive applications of tensile stress on alloy materials. A highly ductile alloy is useful in such an application, because it contributes to the overall workability of the alloy and to the versatility of the forming process. Increasing the ductility of alloys by a modest amount can result in significant cost savings by allowing for a larger range of processing parameters that will not result in undesirable fracturing of workpieces.
Because they exhibit a relatively high strength-to-weight ratio, among a number of other desirable structural features, aluminum and magnesium alloys are of heightened interest in many fields, including automotive engineering. Aluminum and magnesium alloys can be difficult to form into complex geometries, owing to relatively low ductilities and high propagations of defects. For this reason, the alloys often must be processed at elevated temperatures or by using techniques such as die casting or injection molding. One solution might be to seek varying alloy compositions that inherently possess high ductility. However, the efforts spent finding and producing new alloy compositions themselves can be highly cost-prohibitive over attempting to improve the usefulness of existing alloys.
Heat treatments are commonly used in the art to increase the strength and ductility of aluminum and magnesium alloys. Heat treatments may involve processes such as solution annealing, which involves heating alloys to just below the solidus temperature and subsequently quenching the alloys in water or another medium. The heat treatments may involve more elaborate processes comprising very precise temperature ramping schedules that may be combined with physical working of an alloy to increase the elongation of the alloy. Thermal treatments in general can be costly and time consuming.
Hydrogen-induced ductility is a phenomenon known to exist for many titanium-base alloys. Aluminum and magnesium base alloys, however, are generally appreciated in the art of metal forming as being incompatible with hydrogen. Owing in part to several complex physical and electrochemical phenomena, hydrogen can render aluminum and magnesium alloys extremely susceptible to embrittlement and stress corrosion cracking. This is true especially under humid conditions. As such, there remains a need in the art for economical methods to increase the ductility of aluminum and magnesium alloys.